The invention relates to a thermal imaging device for detecting and identifying a thermal object, comprising a rotating IR-transmitting (infrared-transmitting) scanning polygon arranged behind an objective system. The rays which emerge from the polygon are incident on a sensor array which produces electrical signals. The electrical signals are then converted into visible images.
German patent application No. 25 10 733 describes a device for the electronic reconstruction of thermal images. In this device the image, which is focused by means of an IR objective, is scanned with the aid of a rotating IR-transmitting scanning polygon. The scanning polygon is arranged in front of an IR detector array. The electrical signal voltages supplied by the detectors drive light-emitting diodes whose emergent rays, after passing through another polygon which rotates in conformity with the scanning polygon, form an optical image of the thermal scene being observed. In this case the scene is scanned in Cartesian coordinates, the polygon scanning in one coordinate direction only.
From German patent application No. 26 23 373 it is furthermore known to scan a scene observed via an IR objective by means of a pivotable mirror, reversing optics and two prisms which rotate in conformity with each other in Cartesian and polar coordinates. Such an arrangement facilitates the identification of separate objects in the complete IR scene after the detected IR signals have been made visible.
Instead of ocular observation it is also possible to visually display the thermal image on a screen for example on the screen of a picture tube after appropriate signal conversion. Such a device enables one to scan and optically reconstruct the IR scene in two coordinate systems. On the other hand the alignment and control of a mirror demand more mechanical provisions in order to guarantee the necessary accuracy and quality of the derived electronic signals, on which in turn the identification of the thermal objects depends.